Transition metal catalysts, i.e., Ziegler-Natta and metallocenes, generally cannot be practically used for gas or slurry phase polymerization unless sufficiently supported. The use of supported catalysts offers the possibility of gas and slurry phase compatibility. Control of the particle size distribution of the polymeric product in the various polymerization processes eliminates or reduces the extent of reactor fouling.
Supported catalysts for olefin polymerization are well known in the art. These catalysts offer, among other things, the advantages of being useable in gas or slurry phase reactors, allowing the control of polymer particle size and thereby the control of the product bulk density. Gas phase reactors also eliminate the need for a solvent and the equipment for solvent handling during separation of the solvent from the resin. However, it is known that transition metal catalysts, particularly metallocene catalysts, are deactivated by supports that contain reactive functionalities, such as silicas which are oxide supports.
Accordingly, when using supported polyolefin catalysts, it is often desired to remove or reduce hydroxyl groups and other reactive functionalities from the support particles before and/or during manufacture of the supported catalyst. Removal of the reactive functionalities is often desirable since they will often react with the catalyst thereby deactivating it.
For example, in the past, various thermal and/or chemical treatments have been used in an effort to achieve dehydroxylation of the oxide particles.
Thermal treatments (i.e., calcining) are advantageous from the point that they do not add undesirable chemicals to the support and that they are relatively simple inexpensive processes. Unfortunately, thermal treatments are often ineffective for achieving a high degree of dehydroxylation. Further, for many porous oxide supports (e.g., silica gel), thermal treatments often result in an undesirable loss of pore volume, shrinkage of the pores and/or loss of surface area.
Furthermore, a variety of chemical treatments have been attempted to remove or deactivate reactive functionalities. Many types of chemicals have been used such as organo aluminum compounds, magnesium chloride/dehydrating agent combinations, organosilanes, halosilanes, silanes, etc. These various chemical processes are often expensive and may result in the addition of undesired or complicating constituents to an oxide support.
Thus, there remains a need for improved catalytic supports and supported activators having the undesired reactive functionalities deactivated.
Moreover, it is sometimes desirable to impart different characteristics to the support surface. The attachment of selected organic moieties to the support effects the characteristics of the support and hence the catalytic nature of the catalyst and/or activator placed on the support.
Thus it is an object of this invention to provide a method to deactivate reactive functionalities on catalytic supports as well to provide for a new support for transition metal catalysts and a supported catalytic activator.
Furthermore, it is an object of the present invention to provide a supported activator and a supported transition metal catalyst and/or catalyst system (support, activator and catalytic precursor) capable of not only producing polymers, but also providing a catalyst with hydrogen sensitivity so as to allow use of hydrogen to control molecular weight in olefin polymerization reactors.